This invention relates to the manufacture of plastic bags, and more particularly to plastic bags of the type having thereon so-called zipper elements which permit the bag to be repeatedly opened and closed by finger pressure or the like. More particularly this invention relates to an improved machine and associated apparatus for manufacturing such bags.
There are currently available in the marketplace numerous machines for manufacturing zippered plastic bags of the type described. U.S. Pat. Nos. 4,101,355 and 4,355,494, for example, disclose apparatus for producing recloseable plastic bags of the type which utilize so-called zipper fastening elements to permit repeated opening and closing of the associated bag. With these machines the zipper elements are attached by adhesive or by heat fusion to the travelling web or plastic material which is to form the bag. Also, U.S. Pat. No. 4,430,070 teaches the use of hot air for fusing or otherwise securing the cooperating zipper sections to plastic bag material, while U.S. Pat. No. 4,663,915 also discloses apparatus for attaching zipper elements to plastic bag material by use of an adhesive material (for example hot melt adhesive) or by fusion.
In each of the above-noted apparatus, extreme care must be taken to make sure that the proper amount of pressure is applied to the zipper elements as they are fastened to the plastic film or web which is to form the bag. This becomes more difficult in most cases when heat is utilized for fusing the zipper elements to the plastic bag-making film or web. The heat has a tendency to cause metal supporting elements to expand and/or contract different rates, therefore making it extremely difficult to apply uniform pressure to the zipper elements and the film, particularly over extending lengths thereof.
Also it heretofore has been customary to interpose between the heating element and the plastic materials which are to be fused together, a TEFLON element, which prevents the plastic material, when fused, from adhering to the heating element. In those machines in which the attachment of the zipper elements to the bag-making film occurs by advancing the elements and the film continuously in one direction, it has been customary to mount the intervening Teflon element in the form of an endless belt, which travels in the direction of the film and zipper elements. However, the mechanism heretofore employed for mounting such Teflon belts has been rather complicated and unsatisfactory.
It is an object of this invention, therefore, to provide an improved machine for heat fusing zipper elements to the web or film from which reclosable plastic bags are manufactured.
A more specific object of this invention is to provide for a machine of the type described apparatus which minimizes any undesirable distortion of machine parts which might otherwise result from extreme temperature differentials developed in the machine.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.